Select an ISO file, CD or folder containing the extracted LinuxLive ISO's files. If you don't have any ISO or do not know what to install, use the Download button and select a Linux distribution (Ubuntu is a good choice to begin).

It is VERY important to read the Support matrix page for a list of currently supported Linux Distributions.

As an alternative, you can use any IMG file as source but be aware that it will WIPE YOUR DEVICE and you won't have access to any advanced features such as SmartCleaning, portable virtualization ...